In the prior art there are essentially two known types of device converting a rotational movement into a translational movement.
The operation of the first type of device is illustrated in FIG. 1. In that figure there is diagrammatically represented, in a first position 110 and in a second position 111, a device 100 for conversion of rotational movement into translational movement. The device 100 essentially includes:                a first rod 101 forming a link, designed to move in rotation about a fixed rotation axis 103, said rotation being driven by a driver that is not shown;        a second rod 102, designed to move in translation in a translation direction 106 perpendicular to said rotation axis 103; the translational movement of the second rod 102 is produced by the presence in the first rod 101 of a straight opening 104 forming a guide in which a roller 105 fastened to the second rod 102 can move. By causing rotation of the first rod 101, the driver drives the movement of the roller 105 in the guide 104, thus causing the translational movement of the second rod 102.        
In this first type of device, a distance D1 between the translation direction 106 and the rotation axis 103 is constant. Consequently, the lever arm corresponding to a distance D2 between the rotation axis 103 and the position of the roller 105 varies as a function of the position of the first rod 101. There is thus observed an evolution of the direction of a force F1 during rotation of the first rod 101; the change of direction of the force F1 leads to the creation of a mechanical moment on the second rod 102 which increases the friction on the guide 104 of the first rod 101. As the roller 105 moves away from the rotation axis 103, the force F1, as the rotation of the first rod 101 evolves, is in a direction that increasingly departs from the direction of the translation axis 106. There is therefore less and less push on the translation axis 106, the force produced by the driver becoming less and less effective in terms of the push intended to cause translational movement of the second rod 102. Accordingly, in this first type of device, there is observed rapid wear of the various elements (notably the guide 104 and the roller 105), and the energy supplied by the driver is not used optimally.
The operation of the second type of prior art device for conversion of a rotational movement into a translational movement is illustrated in FIG. 2. In that figure there is diagrammatically represented, in a first position 210 and in a second position 211, a device 200 for conversion of rotational movement into translational movement. The device 200 essentially includes:                a first rod 201 forming a link, designed to move in rotation about a fixed rotation axis 203, said rotation being driven by a drive that is not shown;        a second rod 202, designed to move in translation in a translation direction 206 perpendicular to said rotation axis 203; the translational movement of the second rod 202 is produced by the presence, at the level of the upper portion of the second rod 202, of a bearing 204 at the level of which an end 205 of the first rod 201 bears to cause the second rod 202 to descend in a translational movement when the first rod 201 is, in the example considered, driven in a rotational movement in the clockwise direction. The bearing 204 is complemented by an upper part 207 on which the end 205 of the first rod 201 bears to cause the second rod 202 to be raised along the translation axis 206 when, in the example considered here, the first rod 201 is in a rotational movement in the anticlockwise direction.        
In this second type of device, the force applied to the bearing 204 or to the upper part 207 is not constant, and a torque is created at the level of the bearing 204 or the upper part 207, the force exerted by the end 205 becoming more and more off-axis as the movement evolves, as shown by an arrow 208 indicating the direction of pushing on the end 205, the pushing direction 208, which no longer coincides with the central part of the second rod 202. Such a torque has the consequence of wear of the bearing 204 in particular.
The different types of device thus do not enable solutions to be provided in which a constant force, provided by an element or contact of a first rod on a second rod designed to move in translation, is oriented on the axis of said second rod, creating no torque on a contact surface between the contact element and a bearing area of the second rod.